Three-wire telephone system.



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UNITE STATES PATNT OFFRE@ WILLIAM REID, OF CHICAGO, ILLINOIS, ASSIGNORTO KELLOGG SWITCHBOARD da SUPPLY COMPANY, OF CHICAGO, ILLINOIS7 ACORPORATION OF ILLINOIS.

THREE-WIRE TE LE EI'IONE SYSTEM.

To all whom it may concern:

Be it known that l, 'ilinnnnu linie, a citizen of the United States,residing in Chicago, county oit Coeli, and State of Illinois, haveinvented certain new and useful Improvements in rilhree-ldlire TelephoneSystems, of which the following is a specification.

My invention relates to central energy telephone systems, particularlyof the three- Wire type or those in which three contacts are providedupon the jacks and plugs, two of which are in the talking circuit, thethird being used for signaling and testing purposes.

One of the objects ot my invention is to provide a system of this classwhich shall be simple and inexpensive to install while iurnishing thehighest degree of eiliciency in use, and one which shall have itstalking circuit tree from shunts or by-paths other than those necessaryin furnishing the energy to the lines for conversation.

My invention is illustrated in the accompanying drawing in which thehgure represents vo subscribers lines and connective means thereiior atthe central office, with the apparatus shown in its normal orunactuat-ed condition.

In the drawing the subscribers substations 2 and 3 are each providedwith a transmitter 4 and receiver 5 in a bridge of the line conductors 6and 7, said bridge being normally open at the switch hooi; 8 when thereceiver is not in use. A suitable call bell or annunciator 9 andcondenser i() are connected in the permanent bridge of the lineconductors. Any suitable common battery substation outnt may be used inlieu ot that shown.

At the central office the line conductors terminate in levers or contactsprings Il and l2 of the cut-oil relay 13. rElie contact spring 12 isnormally connected to ground and the contact spring Il is normallyconnected with the central ollice battery i4 by means ot conductor l5and the winding of the line relay i6. is controlled through thenormally-open contacts of the line relay in an obvious manner.

Each line is provided with an answering jack having a ring contact ortesting terminal i8 which is connected to one side of the winding ofcut-oil relay 13, the other side of said Winding being connected toground. rlie tip contact spring 19 and the ring spring 20 of theanswering jack are connected withl the Specication of Letters Patent.

Application filed February 26, i906. Serial No. 302,843.

A line lamp or signal i7 Patented Jan. 19, 1909.

normally-open front contacts ol' the cut-oil' relay 13. Multiple jacks2l and 22 are provided in any suitable number.

The operators cord circuit consists oit a tip strand 23 and a sleevestrand 24 extending between the corresponding contacts of the plugs,rlhe tip strand is conductively separated but inductively united by acondenser 25, a condenser 26 being similarly disposed in the sleevestrand. The central o'lice battery 14 is connected in permanent bridgeor the cord strands, a suitable impedance coil 27 being connectedbetween the grounded side of the battery and the tip strand of the cordcircuit upon either side of the condenser 25. rlhe opposite pole of thebattery is connected with the sleeve strand of the cord circuit uponeither side of the condenser 26 through the windings of supervisoryrelays 28 and 29. A supervisory relay 80 is connected with the battery14 by means ci' conductor 31 and with the third contact of the plug bymeans of conductor 32, a supervisory relay 33 being similarly connectedupon the opposite side ot the cord circuit by means of conductors 34 and35. rlhe supervisory lamp 36 is jointly controlled through thenormally-open contacts of the supervisory relay 30 and thenormally-closed contacts of the supervisory relay 28, and thesupervisory lamp 37 is similarly controlled through the correspondingcontacts of supervisory relays 33 and 2Q.

The head receiver, the secondary winding of the induction coil and acondenser are bridged across the strands ci the cord circuit by asuitable listening key 39, and the primary winding 40, in series with atransmitter is shown adapted to be supplied with current from thebattery 14 or any suitable source. A tertiary winding 41 of theoperators induction coil is normally connected between ground and thecontact lever 42 of the supervisory relay 33, said lever being connectedwith the tip strand of the cord circuit, and being normally severed fromsaid strand at the front contact anvil 43 of said relay. A suitableringing generator 44 may be connected with the line by means of aringing key 45 in the usual manner.

'lhe operation ot the system is as follows: The subscriber at station 2,desiring to signal the central oiiice, removes his receiver from thehook, which closes a path for current from the central office battery 14over con- IIC ductor 15, the winding of the line relay 16, theconductors of the telephone line and the substation apparatus to groundat the normally-closed contact 12 of the cut-off relay 13. Current inthis path operates the line relay which attracts its armature and lightsthe line signal 17. Noticing the signal, the o erator inserts heranswering plug in the jack or the calling line. Battery will then ilowthrough the cut-orf relay over conductor 31, supervisory relay 30,conductor 32, ring contact 13, through the winding of the cut-ofi relayto ground. The talking circuit is cempleted at the front normally-opencontacts of the cut-ofi relay 13, due to current in this path, theenergizaticn of said relay also serving to remove the ground from thelimb 7 of the telephone line at contact spring 12, and to remove theconnection of limb 6 with the line relay at contact spring 11, wherebythe line signal is efiaced. rihe circuit or' the supervisory lamp 36 isclosed by the operation of the relay 30, but due to the fact that thesubscribers tele )hone is oif its hook current flows through t iesupervisory relay 23, which opens the circuit oi the lain and preventsits illumination. The )ath 'or current through the relay 28 is over seeve strand 24, the corres onding contact spring 20 of' the jack, theiinbs of the tele hone line, jack spring 19, tip strand 23 an onewinding of the impedance coil 27 to the battery. The operator may nowcommunicate with the calling subscriber by throwing her listening key39. The retardation of the windings of the coil 27 and the sleevesupervisory relays 23 and 29 is adapted to prevent the shunting of thevoice currents through the battery, said voice currents beinginductively propogated from one side of the cord circuit to the otherthrough the condensers 25 and 26. Upon learning that the subscriber atstation 3 is desired the operator tests the condition of said line bytouching the tip of her plug to a testing terminal 1S of a multiple 1arkof that line. If a connection is established with the desired line atanother section ofthe switchboard a potential above that oi ground willexist upon the sleeve oi' the multiple jack tested, due to the ilow ofbattery through said sleeve, as previously described, at the sectionwhere such connecticn exists. Upon testing the line, therefore, a 'liowof battery will result from the test ring oi the jack over the tipstrand of the cord circuit, normally-closed contact 42 of thesupervisory relay 33, through the tertiary winding 41 of the operatorsinduction coil, to ground. This flow of current will vary the potentialacross the bridge containing the operators head receiver, producing aninductive click therein, and notifying her that the line is busy.

lf the line is not in'use the testing terminal 'of the jacks will beconnected to ground through the cut-"ofi relay and no ow of eurrent willresult when the line is tested. Receiving no click in her receiver theoperator will insert the plug in the jack of the desired line. lBatterywill then iiow through the supervisory relay 33 and the cut-ofi' relay13 as previously described with reference to the other side of the cordcircuit, the actuation oi the cut-ofi relay connecting the limbs oi thetelephone line with the jack section thereof, and opening the circuit ofthe line relay to prevent the o eration of the line signal; theoperation o the supervisory relay 33 closing the circuit of thesupervisory lamp 37, and uniting the normally severed tip strand of thecord circuit, at 'iront contact Li3. Due to the fact that thesubscribers telephone is upon its hook the supervisory relay 29 is notenergized to open the circuitl of said signal and the supervisory lamp37 is lighted. The operator now throws her ringing key 45 to signal thesubscriber, the ringing current flowing over the tip contactsoi the plugand jack, line conductor 7, throughv the substation signaling apparatus,line conductor 6, the sleeve contacts oi the jack and plug, and back tothe generator through the sleeve contacts of the ringing key. Upon theresponse of the called subscriber current willflow through thesupervisory relay 29 which will open the circuit of the supervisory lamp37, retiring said signal and indicating that the subscriber hasresponded. rEhe low of current through the supervisory relay 29 is overboth sides of the metallic line and both strands of the cord circuit,returning to the battery through one winding of the impedance coil 27 aspreviously described with reierence to the other side of the cordcircuit. It will be noted that during conversation there are no shuntsor bridges associated with the talking circuit excepting those necessary'for the supplying of energy to the substation transmitters. Eithersubscriber, by replacing his telephone upon the hook, will interrupt theiiow of current through the supervisory relay 23 or 29, which is in thepath of current to the substation, permitting the armature of said relayto drop back, closing the circuit of the corresponding supervisorysignal. The signal is thus illuminated duc to the fact that the circuitsof the supervisory relays 30 and 33 are local to the central or'iice,and Vnot under the control of the subscribers, Y said relays operatingto close the circuits of the supervisory lamps as long as the plugsremain inserted in the jacks. Upon. the termination of the conversationthe operator removes the plugs from the jacks oi the lines, whichrestores all parts to normal condition.

What i claim as new and desire to secure by Letters Patent is:

1. In a telephone system, the combination with a pair oftelephone lines,of a cord circuit or making connection therewith for ioo conversation, aing circuit oi the line normally disconnected therefrom, a signalingapparatus normally connected therewith, a supervisory relay associatedwith the cord circuit, a third conductor isolated from the talkingcircuit, and means associated with said third conductor fordisconnecting said signaling apparatus from the line and closing thecircuit of said supervisory relay, and a signal having its circuitcompleted by the actuation oi said supervisory relay, substantially asdescribed.

2. ln a telephone system, the combination with a pair of telephonelines, oi a cord circuit for making connection therewith forconversation, a third conductor at the central oi'lice isolated from thetalking circuit, a cutoff relay in said conductor, a pair of terminalsin the talking circuit normally disconnected from the line at the irontcontacts oi said relay, a signaling apparatus for the line, asupervisory signal associated with the cord circuit, a pair orsupervisory relays for controlling the circuit oi said signal, oneenergized over said third conductor, and the other over the telephoneline, and means operative in making a connection with the line forcompleting the talking circuit through said terminals, and jointlycontrolling the circuit of said signal through the contacts of saidsupervisory relays7 substantially as described.

3. ln a telephone system, the combination with a pair of telephonelines, of a cord circuit Jfor making connection therewith forconversation, a third conductor at the central oihce isolated from thetalking circuit, a cut-oil' relay in said conductor, a pair oi terminalsin the talking circuit normally disconnected Jfrom the line at the frontcontacts ci said relay, a signaling apparatus for theline, normallyconnected therewith at the back contacts of said relay, a supervisorysignal associated with the cord circuit, a pair oi supervisory relaysfor controlling the circuit ci said signal, one energized over saidthird conductor, and the other over the telephone line, and meansoperative in making a connection with the line for completing thetalking circuit through said terminals, and jointly controlling thecircuit oi' said signal through the contacts oi said supervisory relaTs, substantially as described.

4. ln a telephone system, the combination with a pair of telephonelines, oi" a cord circuit ior making connection therewith forconversation, a third conductor at the central office isolated from thetalking circuit, a cut-oil relay in said conductor associated with theline, a supervisory relay in said conductor associated with the cordcircuit, a pair of terminals in the talking circuit normallydisconnected from the line at the contacts or" said cut-oii relay, acentral source of current, a supervisory signal, means operapair oiterminals in the talkl tive in making connection with the line forcompleting the talking circuit through said terminals at the contacts cisaid cut-oil relay,

f and closing the circuit oi said signal at the contacts oi saidsupervisory relay, and a second supervisory relay receiving current fromthe same side of said source adapted to open the circuit of said signalwhen the subscribers telephone is in use, substantially as described.

5. ln a telephone system, the combination with a pair or telephonelines, of a cord circuit ior making connection therewith forconversation, a third conductor at the central oilice isolated from thetalking circuit, a cut-oil relay in said conductor associated with theline, a supervisory relay in said conductor associated with the cordcircuit, a pair oi terminals in the talking circuit normallydisconnected from the line at the contacts or said cut-oil` relay, animpedance coil, a central source oi current and a second supervisoryrelay in a bridge of the cord circuit, a supervisory signal, and meansoperative in making connection with the line for completing the talkingcircuit through said terminals at the contacts of said cut-oill relay,both of said supervisory relays receiving current from the same side ofsaid source, one oi said relays being energized over said thirdconductor and being.adapted to close the circuit or said signal, theother of said relays being energized over the telephone line and saidimpedance coil, and being adapted to open the circuit of said signalwhen the subscribers telephone is in use, substantially as described.

6. ln a telephone system, the combination with a pair of telephonelines, of a cord circuit ior making connection therewith forconversation, a third conductor at the centra-l oiiice isolated from thetalking circuit, a cutoff relay in said conductor associated with theline, a supervisory relay in said conduc tor associated with the cordcircuit, a pair of terminals in the talking circuit normallydisconnected irom the line at the contacts of said cut-ofi relay, animpedance coil, a central source of current and a second supervisoryrelay in a bridge or" the cord circuit, a supervisory signal, meansoperative in making connection with the line l'or completing the talkingcircuit through said terminals at the contacts of said cut-oil` relay,both of said supervisory relays receiving current from the same side oisaid source, one of said relays being energized over said thirdconductor and being adapted to close the circuit of said signal, theother oi said relays being energized over the telephone line and saidimpedance coil, and being adapted to open the circuit of said signalwhen the subscribers telephone is in use, a second impedance coil, and asecond supervisory relay, said impedance coil and said supervisory relaybeing inlOO ` the cord circuit, a source of current and a thirdconductor, said relays being actuated by current over said thirdconductor when the cord is connected with the line, and a relay coil ina circuit independent of the coils of either of said iirst relays forfurnishing transmitter current to one side of the telephone line and forpreventing the passage of voice currents from the talking circuit, andan impedance coil for furnishing transmitter current to the other sideof said telephone line and for preventing the passage of voice Acurrents therefrom, substantially as described.

8. In a telephone system, the combination with a telephone line, of acord circuit to connect therewith for conversation, said cord circuitand said line circuit each having three contacts adapted to coperatewhen the cord is connected with the line, two of said contacts of thecord and line forming a portion of the talking circuit, the thirdcontact ofthe cord and line being adapted when connected to complete alocal circuit independent of the talking circuit, a cut-oil. relay forthe line in said local circuit, and a supervisory relay for the cord insaid local circuit, a supervisory signal displayed by the actuation ofsaid supervisory relay, and a second relay in a bridge of the talkingstrands ol' the cord circuit adapted to be actuated to efface saidsignal when the cord is connected with a line closed at the substation,substantially as described.

9. In a telephone system, the combination with a connecting circuithaving a pair of talking strands, of a central source of current, animpedance coil connected between one pole of said source and one of saidtalking strands, a supervisory relay connected between the other poleoi' said source and the other of said talking strands, a secondsupervisory relay, and means to actuate it over a path independent ofthe talking circuit, a supervisory signal displayed by the actuation ofsaid latter relay, said signal being adapted to be effaced by theactuation of the former supervisory relay, substantially as described.

l0. The combination with a telephone line, of an operators cord circuit,a source of current, a relay and an impedance coil bridged between thetalking strands of said cord circuit, a second relay lor the cordcircuit adapted to be actuated over a circuit independent of the talkingcircuit g when the cord is connected with a line, said former relaybeing adapted to be actuated over the telephone line when the line isclosed at the substation, and a supervisory signal controlled by thejoint action of said relays, substantially as described.

11. In a telephone system, the combination with a telephone line, of acord circuit adapted to be connected therewith for conversation, asource of current, an impedance coil and a relay bridged between thetalking strands of said cord circuit, a cut-oli relay for the line and asecond relay for the cord circuit, said cut-od rela and'said secondrelay for the cord circuit being adapted to be actuated over a circuitindependent of the talking circuit when the cord is connected with theline, and a supervisory signal having its circuit controlled by theconjoint action of said cord relays, substantially as described.

12. In a telephone system, thecombina tion with a three-conductor cord,of a source of current associated with said cord circuit, an impedancecoil connected between said source and a talking strand of said cordcircuit, a supervisory relay connected between the other pole of saidsource and the other talking strand of said cord circuit, and a secondsupervisory'relay connected between a pole of said source and a thirdstrand of said cord circuit, and a supervisory signal controlled by theconjoint action of said relays, substantially as described.

13. In a telephone system, the combination with a pair of telephonelines, each having talking contacts and a test contact at the centraloffice, a cord circuit for connecting said lines for conversation havingtalking conductors to register with the talking conductors of the line,and a third conductor to register with the test contacts of the linewhen the cord is connected for use, a cut-off relay connected with thetest contact of the line, and a supervisory relay connected with thenthird contact of the cord, said relays being actuated in series when thecordis connected with the line, a second relay associated with the cordcircuit and adapted to be actuated over the telephone line when the cordis con-V nected with a line closed at the substation, and a supervisorysignal displayed by the actuation of one of said cord relays, andveiaced by the actuation of both oi said cord relays', substantially asdescribed.

Signed by me at Chicago, county of Cook, and State of Illinois, in thepresence of two witnesses.

WILLIAM REID.

Vlitnesses:

C. C. BRADBURY, EDITH Gains.

